To a chemist, "base" means the opposite of acid. To the rest of us, "base" means the foundation or starting point. In Total Base Number we are talking about the chemical base, or alkali, condition to neutralize acid. In Base Oil we are talking the 75 or 80% foundation oil to which the additive package is added.
The TBN of new oil indicates a few things, but not a deciding factor. The quality (cost) of the components that create the TBN is more important. The remaining TBN of the oil after it has a lot of miles on it is more important than the starting TBN. Bottom line---buy an oil with an excellent track record, not one with any certain item on its spec sheet.